Vacuum-tube circuits



vJune 24, 1930. E. J. H. BUSSARD VACUUM TUBE CIRCUITS Filed July 27, 1925 ATTORNEYS Patented June 24, 1930 UNITEDASTATES PATENT OFFICE EMMERY J. H. Bussnm or CINCINNATI OHIO, AssIeNoR 'ro THE CROSLEY RAD-I0 CORPORATION, OF CINCINNATI, OHIO, A CO RPORATION OF OHIO VACUUM-TUBE CIRCUITS Application and July 27, i925. Seiiai o. 46,258. 1

My invention relates to vacuum tube circuits and particularly. to circuits known as reflex circuits, where the same tubes are used for both radio-and audio frequency amplification. v I V A known way of reflexing in vacuum tube circuits is to place the secondary of an audio frequency transformer in series in the lead connecting the input-radio frequency circuit to the filament circuit, and impressing upon the primary of the transformer the audio I frequencies from a subsequent rectifying element of the hookup. r

In such a structure the probabilities are that the audio transformer secondary causes the tube in whose input circuit it is in series to rectify, due to the'very great impedance of the secondary to the radio frequency currents. At any rate such an arrangement cuts down the amplitude of the radio frequency currents in the plate circuit of the tube.

It has been the practice in some cases where it was desirable'to amplify or repeat an audio frequency current, to use two vacuum tubes with the in-put to the grids arranged 180 degrees out of phase, thereby resulting in a balancing efiect on the plate circuit currents, due to the fact that there would beno variations in the plate circuits due to unequal actions'of the tubes during periods of positive and negative audio frequency current, be-

7 cause one tube would have a positive and one a negative grid simultaneously.

It is my object to provide for a similar arrangement of tubes to that last above mentioned, but for an entirely difierent purpose, namely to eliminate the high frequency alternations inthe secondary of the transformer used in imposing audio frequencies on the tuned radio frequencies of the pair of tubes, and in connection with the output circuits of the pair of tubes, to duplicate the relation of the input circuits, thereby cancelling the effect of the reflexed audio frequency currents in the plate circuits, of the pair of tubes, so far as concerns their effect on the common radio frequency'transformer in the two output circuits, while at the same time utilizing I will defer further explanation of my invention until I have described a typical circuit in which my invention will be-of value, which circuit or circuits, I will specifically describe and in which it willbe noted that I employ a-pair of tubes in refleXing which are connected out of phase as to radio frequencies, and in in-phase parallel relation to refiexed audio-frequencies, and in directly opposing relation so far as concerns audio requency coupling of the radio frequency output circuit-to subsequent stages of rectification or further amplification.

In the drawing:

Figure 1 isga diagram of one form of hook up.

Figure 2 is a diagram of another form of hookup.

Referring first to Figure 1 it will be noted that the incoming signals are impressed upon the primary 1, and that the opposite ends of the secondary 2 are connected tothe grids 3 and 4 of two thermionic tubes. A lead 5 from the middle of the secondary 2 has the secondary 6 of an audio frequency transformer in series with it andthe lead 7 to the filament circuit ofrthe two tubes. The common lead 5, 6, 7 is the common return of the 'grid circuits to the two tubes, and a tuning condenser Smay be connected across the'twogrid circuits.

In the two tubes the filaments areshown at 9, andthe plates at 10 andll. 5 V

A primary 12'is' connected to the two plates,

and from .thep'rimary central point a common return lead for the two plate circuits as at 13, has an audio transformer primary 14 in series therewith. Thus the two tubes have their input and also their output circuits connected 180 degrees out of phase. I show a detector tube with grid 15, filament 16 and plate 17 pressed upon it, a radio frequency voltage by means of the secondary 18, which is coupled with the primary 12. The plate circuit with lead 19 has in series therewith the primary 20 which is coupled with the secondary 6 forming an audio frequency transformer with the core'21. 7

An audio frequency amplifying tube. is

The gridhas ime degrees out of phase relation, and the lead in common to the two grid circuits, comprising leads 5 and 7 and the secondary 6, instead of having a rapidly pulsating current therein, has a substantially steady current due to the out of phase relation, thereby cutting downthe rectifying action of this secondary.

The plate circuits of the two paired tubes, whereas they act out of phase on the primary 12, pass in opposite directions from the ends of the primary to the middle, so that the radio frequency currents have a common inductive effect on the secondary of the rectifying tube grid or input circuit.

The rectifying tube plate circuit impresses on the primary 20, an audio frequency which is inductively effective on the secondary 6-, thereby reflexing the audio frequency on the two paired tubes, but in this instance the audio frequencies are in phase in'the two grid or input circuits, as are the resulting audio modulations in the two plate circuits or outputs of the paired tubes. 7

The amplified audio frequencies in the primary 12, which are so built up have no inductive effect on the secondary 18, however, because they flow in opposite directions from ends to the middle of the primary 12, thus cancelling the inductive effects of each other on the secondary 18.

However, in the primary 14, the output audio frequencies are in phase with each other and thus impress upon the secondary 26 in the grid circuit of the audio amplifying tube, the amplified audio frequencies which were reflexed backf-rom the detector unit. Y

Instead of cutting down the impressed voltages in the grid circuits of the'pa-ired tubes to half the voltage of a full connection,the result of connecting the grids each to but one half of theinput secondary gives a good deal more than half the voltage'on each grid. This arises from the fact that with the grid circuits of high impedance of the type as shown, and a tube of the usual low input impedance to be found in commercial tubes of the present day, there is a better balance of impedances Where only a portion of the input secondary is used than where all of it is used.

In the circuit shown in Figure 2 the input secondary 40 is connected from a middle point by leads 41 and 42 with a series connected audio transformer secondary 43 be onda1'y 43 and the core 51 make up the reflexing 'audio, frequency transformer, is in the output circuit of the rectifying device.

I have not drawn out the rectifying circuits as these have been shown in Figure 1,

and this second hook up differs from the first in that there is no stage of audio frequency amplification except that which is provided by the reflexed tubes.

In each instance the pairof audions are connected out of phase for radio frequency amplification, and in phase for audio frequency amplification with the result that the audio frequencies are out-of phase in the input and output radio frequency transformers and the radio frequencies are out of phase in the input and output audio frequency transformers. I do not find that there is any unsymmetrical action of the paired tubes due to the audiofrequencies being sent through the paired circuits in inphase parallel relation.

In the claims, it will be understood that a single audion with two plates and two grids is consideredthe equivalent of two audions of the'usual three electrode type. 7

Having thus described my invention, what I claim as new and desire to secure by Letters Patent, is

1. in an audionamplifier, two audions connected in out-of-phase parallel relation for radio frequency amplification, and in-phase parallel relation for audio frequency amplification, the plateterminals of said tubes connected each to opposing terminals of a radio frequency inductance, the center point.

of said radio frequency inductance being connected through a device sensitive to audio frequency signals, and a source of plate potential to the common filament 'circuit of the said audion tubes, means for rectifying and amplifying the modulated radio frequency current in the said plate inductance and impressing the resulting audio frequency current on the primary of a transformer, the secondary of which is connected in the common grid filament lead of the said audion tubes.

2. In an audion amplifier,two audions connected in out-of-phase parallel relation for radio frequency amplification, and in inphase parallel relationship for audio frequency amplification, the plate terminals of said tubes connected to opposing terminals of a radio frequency inductance, a center tap of said radio frequency inductance being connected through an audio frequency impedance and a source of plate potential to the common filament circuit of said audions,

means for amplifying and rectifying the current of said plate circuit and impressing the resulting audio frequency voltage by means comprising a reactance, upon the common grid-filament lead of the said audion tubes.

3. In an audion amplifier, two audions connected in out-of-phase parallel relation for radio frequency amplification, and in inphase parallel relation for audio frequency amplification, the plate terminals of said tubes connected to opposing terminals of a radio frequency transformer, a center tap of said radio frequency transformer being connected through the primary of an audio frequency transformer and a source of plate potential to the common filament circuit of said audions, means for amplifying and rectifying the current in said plate circuit and impressing the resulting audio frequency voltage upon the primary of a transformer, the secondary of which is connected to the common grid-filament lead of the said audion tubes.

EMMERY J. H. BUSSARD. 

